Is Pluto a "proto-planet"?

  • My question is this : could the Charon-Pluto system becomes in the coming few millions years a full fledged planet, as in the IAU classification ?



    I ask this because there are two facts that bother me :




    • The system orbit isn't on the ecliptic

    • The system hasn't cleared its neighborhood



    So, is it possible that that system isn't stabilized yet, and that 1) its orbit is very slowly changing (for lack of a better word) to the ecliptic, and 2) that the system will slowly collapse, and bring all its moons with it, to clear its neighborhood ?



    In other words, is Pluto a "proto-planet" (as I would personally name it), or definitely (and for the next millions years) a dwarf planet ?



    Edit : I disagree on the fact that this question is a duplicate of How long will it take Pluto to grow to planet size? as this one ask not for the size of Pluto, but rather the other characteristics, the orbit and the clearing the neighborhood.

    Moreover, the question was asked in a broader canvas, to know if it was possible that some elements of the solar system (Pluto, but not only) could be instable enough to reach the level of planet sometime in the futur.


    Generalizing the question a bit, one could ask if any of the known trans-Neptunian objects might ever become a "planet". That gets around the "what would we call the result of an Eris-Pluto merger" problem. Generalizing even further, it might be worthwhile to ask whether there is some yet undiscovered body in the outer solar system that does meet the definition of a planet. That's not a good question for this site. The only possible answer is "We don't know (but we've ruled out a number of possibilities)."

    @called2voyage are you saying it is not possible to define what amount of mass in the Kuiper belt would be required to form a single body that meets the re requirements of the IAU definition of planet?

    @JamesJenkins I'm saying that it is not the mass that is important but whether or not the orbit is clear.

    So because the orbits of Pluto and Neptune overlap Pluto can't ever be a planet no matter how big it gets? If that is case how is Neptune a planet? Or is that a different question?

    @JamesJenkins Neptune is gravitationally dominant, see this Wiki article. Yes, mass plays a role, but there is no absolute mass limit for a planet; that's what I'm trying to say.

    called2voyage, I agree, except that the other post didn't really answer the question. In particular, the answer I got below answered it much better in particular with the quote "They will never be able to clear their orbits because Neptune dominates the area." which was much better than "No". In any case, I trust your judgement. I just believe that the answer wasn't given in the other post, and that's why I asked my question.

    @Cqoicebordel You have made a good case. Your question was better formulated than the other, so I have made the other a duplicate of *this one* and merged the questions.

  • Andy

    Andy Correct answer

    6 years ago

    The question says a few interesting things:




    • The system orbit isn't on the ecliptic

    • The system hasn't cleared its neighbourhood



    These are not going to change in the next few million years - or ever.



    Orcus is an interesting counter-example. It is in a similar orbit to Pluto - similar aphelion, perihelion and eccentricity, similar orbital period (to within a year or so) and an inclination of around 20 degrees, a little more than Pluto.



    In short, in orbital terms Orcus is as much a planet as Pluto is - except of course it's only around half the diameter and has far less mass.



    Pluto is never going to displace Orcus from its orbit. In fact they were both pushed into their orbits by Neptune and the Kozai mechanism, which causes its inclination. They will never be able to clear their orbits because Neptune dominates the area.



    To answer the final part of the question - Pluto is officially regarded a dwarf planet by the current definition. Partly because of its orbit as your question states. Whether it's also a protoplanet or not may be debatable. I'd say it's too big to be considered a protoplanet because it's too big. (The larger asteroids like Ceres, Vesta etc. are probably closer to that size range.)


    Thanks for your answer, which is very clear :) Except for the last sentence : Pluto won't be a protoplanet because it's _bigger_ than Ceres and Vesta ?

    @Cqoicebordel thanks - I've edited a bit as I wasn't clear about the size considerations. (Pluto is probably too big to be considered a protoplanet, though I'm not aware of any "rules" on what size range a protoplanet would be.)

    I'm sorry, but your clarification isn't helping me a lot : intuitively, I would say bigger means more mass. More mass means more chances of clearing its neighborhood. So, following that logic, Pluto has more chance to become a planet than Ceres, Vesta etc. which would make it a protoplanet. So, what am I missing here ? Is there an "official" protoplanet classification I didn't know that you are talking about ? Or is there another celestial mechanism (you didn't mention above) that would prevent Pluto gaining mass because it's too big already ? In any cases, thanks for your answers :)

    @Cqoicebordel that's OK. In the first part, I'm saying Pluto's orbit is unlikely to change much, as Neptune is effectively controlling its orbit. In the second half, I understand "protoplanets" to be the small building blocks of a few hundred kilometres across, that later formed planets. Some of the asteroids are said to be protoplanets, but Pluto is much larger than them and should belong to a different class; though I don't believe there is a **formal** definition of a protoplanet size.

    Ok, now I understand. I was using the term proto planet as "could evolve to become a planet". That's why I didn't understand you. Thanks for the clarification ! :)

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Content dated before 7/24/2021 11:53 AM